New Oxypyridinate Paddlewheel Ligands for Alkane-Soluble, Sterically-Protected Ru2(II,III) and Ru2(II,II) Complexes.

Abstract

The paddlewheel complex Ru2(chp)4Cl (1-Cl, chp = 6-chloro-2-oxypyridinate), upon reduction with Zn, has been previously shown to dimerize to [Ru2(chp)4]2 (2), blocking further chemistry at the Ru2(II,II) axial site [ Inorg. Chem. 2015 , 54 , 8571 - 8589 ]. Functionalization of the chp ligand at the 3 and 5 positions with either bromine (dbchpH = 3,5-dibromo-6-chloro-2-pyridone) or trimethylsilyl (TMS) groups (dsichpH = 6-chloro-3,5-bis(trimethylsilyl)-2-pyridone) allows for the preparation of the Ru2(II,II) paddlewheel complexes Ru2(dbchp)4 (3) and Ru2(dsichp)4 (6), respectively, neither of which shows evidence of dimerization. Though the utilization of 3 is limited due to insolubility, complex 6 is soluble even in typically non-coordinating solvents, forming a stable κ1-axial adduct in CH2Cl2 (6-CH2Cl2) and showing evidence of an axial interaction with n-decane. The first example of an axially free Ru2(II,II) complex with a 3A ground state is observed upon crystallization of 6 from benzene (6-C6D6). Complex 6 is accessed via Zn reduction of Ru2(dsichp)4Cl (4-Cl), which along with Ru2(dsichp)4N3 (4-N3), show similar structural and electronic properties to their non-TMS-substituted analogues, 1-Cl and 1-N3. Photolysis of 4-N3 in frozen solution generates Ru2(dsichp)4N (5); no N atom transfer to PPh3 is observed upon room temperature photolysis in fluid solution.